That's an illuminating postmortem - thanks for sharing.
With regard to the hardness of puzzles - I just think the expectations of text adventure players these days are for games to be a lot more merciful. As I said elsewhere, I had a very similar experience when making a game where the required path to victory seemed blindingly obvious and well-clued (to me) but my players really struggled with it (originally, I included no puzzle-specific help or hints). Similarly, before writing it I had no substantial recent experience of playing text games (I more or less left them behind when I was, say, 14 and I'm now 44) so my intuitive idea of what difficulty level was acceptable to today's players was someway off the mark. Nowadays, if a game doesn't include a metaphorical big red emergency escape button to get past a difficult puzzle then that in itself makes it seem quite old-school.
With the hints that you've now put in the game: they are helpful, but I'd still urge you to include (at the end, or alongside) an explicit solution if someone (like me) just really isn't getting it. For an example of such a situation: in the locked bedroom (which I got out of eventually), without any hints at all I had found the hanger, unscrewed the hook, inserted it into the door to pry the latch, found the cane and removed the cap. I then spend some time trying to LEVER HOOK, ATTACH CANE, ATTACH CANE TO HOOK, LEVER HOOK WITH CANE, ATTACH HOOK TO CANE all to no avail. The explicit thing that I had to do (which is not stated in the hints) simply escaped me. I managed to do the right thing in the end, because I felt enough investment in the game to persevere, but many other similarly puzzle-inept players would simply have given up and walked away to play something else - and never seen all the hard work that you put into the rest of the game. I'd say that it is worth offering the last resort nuclear option ('just tell me exactly what to do so I can get to the next bit please!') to prevent that outcome.